Telegraph distributors



pil Z1, '1959 H, D GAlTE 2,883,455

TELEGRAPH DISTRIBUTORS Filed April 20, 1955 ,5 SheefsLSheet 1 pso nv LO PHASE smv-'T DQWER VALVE osclLLAToR I HoLmNG HV MULTI VIBRATOR vALve EMV T III-H 2 BRIOGE QATE.

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` TELEGRAPH DISTRIBUTORS Filed April 20, 1955 5 Sheets-Sheet 2 FIG. E.

April 21, 1959 H. D. GA'ITE 2,883,455

TELEGRAPH DISTRIBUTORS Filed April zo, 1955 '5 sheets-sheet s H. D. GAITE TELEGRAPH DISTRIBUTORS April 21, 1959 Filed April 20, 1955 5 Sheets-Sheet 4 A VA' v for Apdril 21, 1959 l H. D. GAITE I 2,883,455

'TELEGRAPH DISTRIBUTORS Filed April 2o. 1955 .5 sheetssheet 5 United States Pater TELEGRAPH DISTRIBUTORS Harold D. Gaite, Taplow, England, assignor to British Telecommunications Research Limited Application April 20, 1955, Serial No. 502,584

Claims priority, application Great Britain April 27, 1954 6 Claims. (Cl. 178-53.1)

The present invention relates to electrical switching arrangements .and particularly those suitable for use as telegraph distributors. The main function of such `a distributor is to ensure that signals which are generated simultaneously shall be distributed so that they are passed successively to line and in telegraph equipment as at present in use it is also desirable that the distributor should perform certain secondary functions, particularly the stepping of the coder or tape reader from which the signals are derived.

Initially it was found satisfactory to employ for this purpose mechanical distributors comprising essentially brushes which were rotated at a fixed speed over .a suitable number of contacts. With the development of the art however, it is now known that the required effects can be more satisfactorily produced entirely electronically and it is generally preferable to dispense with rotating equipment and to take advantage of the more liexible .and simplied control which electronic operation permits. The object of the present invention is to provide an improved telegraph distributor of the electronic type which is simple to operate and offers advantages on the ground of compactness.

According to the invention, in a distributing arrangement for use in `a start-stop telegraph transmitter, operating pulses for effecting the control of a transmitting relay are obtained from a counting ring yof valves arranged to be operated by pulses obtained alternately from the cathodes of the two valves comprising a multivibrator which is locked to a constant frequency source.

The invention Will be better understood from the following description of a preferred method of carrying it into effect which should be taken in conjunction with the accompanying drawings comprising Figs. 1-5. Of these, Fig. l is .a block schematic indicating the general lay-out of the distributor and the interconnection of the various circuit elements, while Figs. 2-5 represent Ia complete circuit diagram. These figures should be arranged with Fig. 4 below Fig. 3, Fig. 2 on the left and Fig. 5 on the right.

The operation will be `described for transmission :at a speed of 50 bauds under the control of .a tape reader or coder. It is assumed that the system operates on la 71/2 unit basis and hence that the start element and the live coding elements each have a length :of 20 ms. and the stop elements has a length of 30 ms.

As may be appreciated from Fig. l, the basic timing is effected from the 100 c./s. phase shift oscillator PSO which produces .a sinusoidal waveform which is applied to the driver valve DV where it is squared and passed on to the locking oscillator LO. This :is a toggle circuit of conventional type and serves to produce squared waveform pulses at 50 per second which are applied to the drive of what may be termed an 8-phase multivibrator or triode counting ning EMV. This consists of four double triodes and in each complete cycle produces a series of eight negative output pulses.

The rectangles G1-G5 indicate gate circuits each com- HCC prising a D.C. bridge including va rectifier the bias of which is determined from the -coding contacts of a coder" or the contacts of a tape reader controlled by the peckers. These contacts are designated Pl-PS. If the contacts rare closed, the bias is altered so that the gate circuit is closed and the pulse from the unit EMV does not pass to the :output circuit OC.

The rectangle B represents a similar D.C. bridge circuit but in this case no variation of bias is needed as the gate is required to be permanently open. It will be appreciated that this corresponds to the start pulse the nature of which is invariable.

The output circuit OC comprises a double triode connected yas a conventional toggle with the opposing wind ings of the output relay connected in the respective anode circuits. Suitable bias is provided so that the output relay normally occupies the mark position.

When sending is to take place, the first pulse from the unit EMV forms the start element of a character and is applied by way of the bridge B to the output circuit OC. The output relay is thereupon reversed anda space signal is sent over the line L. The next tive pulses from EMV are applied respectively to the gates Gl-GS and according as these are open or closed dependent on the state of the pecker control contacts, pulses are or are not passed to the output circuit. The seventh pulse from EMV is applied to a so-called timing valve TV which serves to double the speed 'of openation tof the locking oscillator LO until the beginning of the next pulse so that the pulse in question is of l0 rather than 20 ms. duration. The eighth pulse is applied to a pulsing valve PV which serves to deliver a 20 ms. pulse over lead SM to the stepping magnet of the coder or tape reader to advance it to the next reader position. The seventh and eighth pulses are not applied to the output circuit and Iaccordingly the bias on the transmitting relay ensures that a mark signal forming the stop element is transmitted to line `during the 30 ms. period represented by the sum of the two pulses.

The bridge network represented by Z in Fig. 1 is gated by a control circuit which may comprise the tape sensing and tight tape switches of the tape reader connected in series, these contacts being collectively indicated at T in Fig. 1. When both of these contacts are closed, the holding circuits are inoperative and the -distr-ibutor functions normally. When either set of contacts is open however, the holding valve HV and timing valve TV oooperate to hold the locking oscillator LO inoperative after the `distributor has reached the appropriate position in this cycle, that is to .say as soon las the seventh pulse commences. This is effected by way of a gas discharge tube indicated at HG.

Considering now the detailed circuit represented by Figs. 2-5, the phase shift oscillator is comprised by valve Vla, Fig. 2, in association with the cathode follower valve V111, Fig. 3, which has a low impedance output `and thus reduces the load :of the succeeding driver stage V21: on the oscillator. The anode of valve Vla is connected to the grid of valve Vlb by way of resistor R10 and lead 8 and feedback from the cathode of Vlb takes place over lead 9. The oscillator network components comprising capacitors C1, C3, C4, C5, C28 and resistors R6, R9, R11, R12 and RVl are chosen to give the required 360 phase shift at c./s. .and are .arranged so that the phase is advanced across each resistance-capacitance network in turn to maintain the oscillator in a state of oscillation. The small capacitor C28 has a negative temperature coeiiicient to mitigate the effect on frequency of temperature changes, and a tine adjustment is provided by the variable resistor RVI.

The output from the cathode of valve V1b is capacity coupled by way of C7 to the driver valve V2b which produces from its anode squared waveform pulses to drive the locking oscillator. The neon tube V11 connected between the cathode of VZb and earth serves to permit convenient checking of the speed of the oscillator, the flashes from the neon tube being viewed through a stroboscope tuned to 100 c./s.

The locking oscillator comprises a multivibrator formed of the double triode V3a, V3b with its two anodes and grids cross-connected in conventional manner by way of capacitors C12 and C15 to operate at 25 cycles per second and give positive pulses alternately from its cathodes for every other pulse applied from the anode of valve V2b by way of capacitors C9 and C10 these pulses producing a synchronising effect. It will be noted that the frequency of the oscillator is four times that of the multivibrator so that only alternate pulses from the oscillator are effective. The pulses from the cathode of valve V3a are applied over lead 15 to the grouped cathodes of valves V6b, V7b, VSb and V5b, Figs. 4 and 5, in the S-phase multivibrator or counting ring EMV comprising the four double triodes VS-VS. Similarly pulses from the cathode of valve V3b of the locking oscillator are applied over lead 16 to the grouped cathodes of valves V611, V7a, V8a and VSa.

The 8-phase multivibrator or counting ring comprises four double triode valves V-V8 with which are associated resistance bridge networks whereby a negative pulse may be obtained from one of the anodes of the ring for each input pulse received from the locking oscillator. At any instant all valves of one group Will be nonconducting because the cathode potential of that valve and the other three valves connected thereto will be high due to the conduction of that valve of the locking oscillator which shares the cathode resistor, the anode resistors of the locking oscillator being of lower value than those of the counting ring. At the same time, the other valve of the locking oscillator will be non-conducting so the cathode potential of the four valves forming the other group will be low but one will be conducting sufciently to hold the other three non-conducting. At the end of its time period the conducting valve will be caused to cut off and a positive pulse derived from its anode will be applied to the grid of the valve next in sequence in the other group having a low cathode potential. This valve accordingly conducts and the cathode potentials of the two groups of valves are reversed. In this manner each valve in turn is caused to conduct in a predetermined sequence by a positive pulse from the anode of the preceding valve at the same time as the locking oscillator changes over. The pulse obtained when the rst valve V6a of the counting ring conducts forms the start element of a character and the next ive pulses form the live coding elements. As explained above the seventh pulse is of 10 ms. duration while the eighth is again of ms. duration and these two pulses together form the ms. stop element.

The coding pulses from the first six valves V6, V7, and V8 of the counting ring are applied to rectiers MR5-MR10. Each rectifier is connected to the middle of a D.C. bridge in the corresponding valve circuit, the bridge in the case of valve V6@ being formed by resistors R19 and R20 connected between the anode of the valve and negative HT connected to lead 11. The junction of R19 and R20 is at approximately earth potential when the valve is non-conducting. The rectiers are controlled over leads 1-5 connected to pins 1-5 of the socket SKB, Fig. 2, into which a plug is inserted so that these leads are extended to the pecker-controlled contacts P1-P5, as indicated more clearly in Fig. l. When a pecker contact is closed, an earth connection is made to the corresponding bridge circuit and holds the junction at earth when the valve conducts. As a result, the corresponding rectifier does not conduct and thus no negative pulse is transmitted over lead 12 to the Cil 4 grid of the output valve V917 and hence the transmitting relay is not reversed. On the other hand if the pecker contacts are open, this earth connection is not present so that the rectier is able to conduct and a negative pulse is applied over lead 12 to the grid of valve V9b to cause the changeover of the transmitting relay.

The valve V4b, Fig. 5, conducts while any of the valves of the counting ring except valve VSa is conducting. When valve Va conducts at the beginning of the seventh pulse, the negative pulse derived from its anode is applied over resistor R62 to the grid of Valve Vb and causes it to cut oil. Thereupon the increased potential derived from the anode circuit of valve V4!) extends over lead 13 and increases the potential of the grids of the valves Va and V3b of the locking oscillator so as to cause it to operate at twice its normal speed so that it produces only a l() ms. pulse before its next changeover.

Neon tube V12, Fig. 3, is connected by Way of lead 17 between the grid of valve VSa and lead 6 extending over pin '7 of socket SKB to the tape sensing contacts (T, Fig. 1). Under normal running conditions tube V12 is extinguished since there is earth applied to pin 7. If however the tape sensing contacts are open, earth is removed from this pin but the potential of the junction point of resistors R57 and R83 changes little until valve V4b is `driven non-conducting as just described, whereupon this potential rises sufciently to cause the tube V12 to strike. Thereupon it applies positive potential to the grid of valve VSw so that this valve remains conducting. Valve V4a also is affected by these conditions in that its grid is driven positive and it then conducts and forms a low impedance to reduce the potential of the grid of valve V3b which is therefore held non-conducting as its cathode potential is held up by the current of valve VSa through resistor R48. At the same time valve V3a is held conducting as its grid is held positive by way of resistors R38 and R65.

The output control circuit to which pulses are supplied over lead 12 and rectiers MR5-MR10 comprise a conventional toggle circuit consisting of the double triode V9. The coils of a known type of telegraph relay are connected in the anode circuits of these valves over the switching base SKD and it will be seen that the relay RLA is shown as provided with six coils, only four of which are used in this particular application.

Valve V9a is normally biased to cutoi by negative potential applied by way of resistor R78 with the result that the relay contacts are held in the mark condition, valve V9b being conducting. When a negative pulse is applied to the grid of this valve, for instance by way of one of the rectiiers MR5-MR10, the valve is cut off and valve V9a then conducts and the relay changes over to its alternate position.

At the beginning of the eighth pulse from the ring counter when valve VSb starts to conduct, a negative potential is applied to the grid of the valve V2a, Fig. 2, by way of resistor R68 and lead 13 and this valve accordingly cuts oft and thereupon applies a positive pulse by way of capacitor C2 to the grid of valve V10. This thereupon conducts and transmits a negative pulse over pin 12 of socket SKB to operate the driving magnet of the tape reader or coder. This pulse is terminated 20 ms. later when in synchronism with the next pulse from the locking oscillator, valve V5.6 is cut o' and consequently valve VZa again conducts and cuts off valve V10.

Since the distributor may lbe remote from the operating position, provision is made to plug a reader or keyboard coder directly into the distributor by way of socket SKA. To simplify switching, the pecker connections of the coder socket SKA have been wired in parallel with those leading to the tape reader or switching base via socket SKB. As some of these latter may be earthed, it is necessary to arrange that only one plug can effect the necessary control and if both sockets should be plugged up simultaneously it is arranged that the line is held at mark and no driving pulses are delivered. For this purpose it is arranged that any plug inserted in socket SKB has pins 8 and 10 linked, thus extending HT potential, which is normally extended over lead 14 to pin 10, to pin 8 which is connected to pin 18 in socket SKA. All coders which are used in this socket must have either pin 8 or pin 11 connected to pin 18 and these two socket pins are Wired together. Hence if two plugs are inserted, HT is extended to resistor R14 and via rectifier MR3 to the grid of valve V2a. This valve accordingly cannot be cut ol by the fall of potential normally produced by valve VSb but remains conducting so that valve V is unable to produce the necessary drive pulse. Moreover HT is also extended over rectifier MR14 and lead 12 to the grid of valve V9b which is thus maintained conducting and hence holds the output at mark.

There may be other circumstances in which it is desired intentionally to hold the output at mark and this is taken care of by the potentiometer formed between HT positive on lead 7 and HT negative on lead 11 by way of resistors R89, R90 and R91 the values of which are such that the junction of R89 and R90 is normally slightly negative. Rectifier MR4 thus isolates this point from the grid of valve V9b. However if earth is applied to pin 11 of socket SKB which is connected to the junction of resistors R90 and R91, the anode of rectifier MR4 is made positive and it accordingly conducts to apply positive to the grid of valve V9b and thus hold the output to mark. If it is desired to hold the line at space, positive is applied to pin 9 of socket SKB and this is extended over lead 10 and resistor R85 to the grid of valve V9a which causes it to conduct and thus hold the output relay at space.

An alternative arrangement for producing the same result with earth connections only is to form a potentiometer between HT positive and HT negative by connecting in series four resistors of such value that the mid point is approximate at earth potential and this point is connected to the grid of valve V9a by way of a neon tube. If the junction point of the rst and second resistors is now earthed, the potential of the mid-point to which the neon tube is connected is lowered suiciently to cause the tube to strike and thereby hold valve V9a non-conducting so that the output is held at mark. Similarly if the junction point of the third and fourth resistors is earthed, the potential of the neon tube is raised and it again strikes but in this case holds valve V9a conducting so that the output is held at space.

The test switch TS shown in Fig. 2 is normally in the position shown when the distributor is being controlled from a tape reader connected to socket SKB. If control is to be from a coder connected to socket SKA, the test switch is operated and earth is then connected from pin 13 of this socket to provide the connection to lead 6 normally supplied over the tape sensing and tight tape contacts and thus permit operation to take place.

The distributor may be used in conjunction with a keyboard and in these circumstances it is necessary to ensure that the distributor makes one cycle only each time a key is depressed. Negative potential from lead 11 which is normally connected to pin 13 of socket SKB is extended over resistor R79 to pin 15 from which it is further extended to the keyboard and over contacts closed whenever a key is depressed and is returned to pin 7. This connection is extended over lead 6 to the neon tube V12 as already described and releases the hold `circuit for about ms. so allowing the distributor to complete one cycle only.

The power supply arrangements shown on the right of Fig. 5 includes a series-parallel arrangement of the primary of the power transformer TR1 so as to cover the range 100-150 volts and 20G-250 volts for the mains supply. Rectification for the HT supply is elected by means of the valve V13 fed from the centre-tapped secondary, smoothing being etected by capacitors C30, C31 and C21, choke L1 and capacitors C20 and C29. The HT negative potential connection is provided in a circuit from one Iend of the transformer secondary by way of resistor R and rectiliers MR11-13.

I claim:

l. In a telegraph system employing a start-stop code, an electronic distributor comprising a constant frequency pulse source, a pair of valves connected as a multi-vibrator, connections between said source and said multi-vibrator, a plurality of valves connected to form a counting ring, means for supplying pulses alternately from the cathodes of the two valves of said multi-vibrator pair to cause a different valve in said counting ring to be rendered conducting in response to each successive pulse, a like plurality of gate circuits arranged to control the respective outputs of the individual valves of said plurality, control leads for said gate circuits, means for selectively applying potentials to said control leads under the control of transmitting equipment to open said gates in accordance with the desired signals, a transmitting relay, and means for operating said transmitting relay each time a pulse from one of the valves of said counting ring passes through the associated gate circuit which has been opened by the application of potential to the associated control lead by said transmitting equipment.

2. In a telegraph system employing a start-stop code, an electronic distributor comprising a constant frequency pulse source, a pair of valves connected as a multi-vibrator, connections between said source and said multi-vibrator, a counting ring comprising eight Valves having their cathodes connected together in two groups of four, means for supplying pulses alternately to the two groups of multipled cathodes from the cathodes of the two valves of said multi-vibrator pair respectively to cause a different valve in said counting ring to be rendered conducting in response to each sucessive pulse, six gate circuits arranged to control the respective outputs of the iirst six valves of said counting ring, control leads for said gate circuits, means for selectively applying potentials to said control leads under the control of transmitting equipment to open said gates in accordance with the desired signals, a transmitting relay, and means for operating said transmitting relay each time a pulse from one of the valves of said counting ring passes through the associated gate circuit which has been opened by the application of potential to the associated control lead by said transmitting equipment.

3. A distributor as claimed in claim 1 including means responsive to the conduction of a particular valve in said counting ring for causing the speed of operation of said multi-vibrator to be doubled.

4. In a telegraph system employing a start-stop code, an electronic distributor comprising a constant frequency pulse source, a pair of valves connected as a multi-vibrator operating at a frequency which is a small sub-multiple of the frequency of said source, connections between said source and said multi-vibrator, a plurality of valves connected to form a counting ring, means for supplying pulses alternately from the cathodes of the two valves of said multi-vibrator pair to cause a different valve in said counting ring to be rendered conducting in response to each successive pulse, a like plurality of gate circuits arranged to control the respective outputs of the individual Valves of such plurality, control leads for said gate circuits, means for selectively applying potentials to said control leads under the control of transmitting equipment to open said gates in accordance with the desired signals, a transmitting relay, and means for operating said transmitting relay each time a pulse from one of the valves of said counting ring passes through the associated gate circuit which has been opened by the application of potential to the associated control lead by said transmitting equipment.

5. A distributor as claimed in claim 3 including a control valve, means for rendering said valve normally conducting, means for cutting off said control valve responsive to a pulse from said particular valve in said counting ringr when it becomes conducting and means responsive to the cutting o of said control valve for raising the potential applied to the grids of the tWo Valves constituting said multi-vibrator whereby the speed of operation of said multi-vibrator is doubled.

6. In a telegraph system employing a start-stop code, an electronic distributor comprising a constant frequency pulse source, a multi-vibrator and a counting ring of valves which are caused to conduct one at a time in turn, a regular socket, a tape reader, a irst plug connected to said tape reader and suitable for insertion into said regular socket, a test socket, a coder, a second plug connected to said coder and suitable for insertion into said test socket, and interconnection between the pins of said plugs and between the contacts of said sockets, a first control valve, means responsive to the cutting on of a particular valve in said counting ring for reducing the potential of the control grid of said firs't'V control valve and thus causing it to cut-off, a second control valve having its control grid connected to the anode of said rst control valve whereby said second control valve is caused to conduct when said rst control valve is cut-off, a driving circuit for said tape reader and said coder including the anode of said second control valve, and means including said interconnections for connecting positive potential to the grid of said first control valve to cause it to remain conducting and thus prevent said second control valve becoming conducting and driving Said tape reader and said coder.

References Cited in the ile of this patent UNITED STATES PATENTS 2,412,642 Wilkerson Dec. 17, 1946 2,612,562 Baker Sept. 30, 1952 2,623,948 Hansen Dec. 30, 1952 2,687,451 Slayton Aug. 24, 1954 2,732,428 Dain Ian. 24, 1956 2,806,901 Ferguson Sept. 17, 1957 

